In transmission of data over a CAN bus, the maximum capacity utilization of the bus in practice is usually approximately 50%. Among other things, this is due to the protocol overhead of the physical protocol required by the CAN bus, i.e., the header part of CAN messages may be larger than the useful data part or payload part of the message. For example, if the DLC (data length code) is 8, then 64 payload bits and 1+12+6+16+2+7=44 header bits are provided. The ratio may be worsened by stuff bits.
In addition, the maximum feasible transmission rate of a CAN bus at the present time is limited to approximately 1 Mbit/sec (106 bits per second) due to physical boundary conditions and in particular due to delays on the CAN bus. This corresponds to a minimum bit time of 1 μsec (10−6 seconds). At a higher transmission rate, problems may occur in CAN bit arbitration which prevents collisions among messages, because the signal transit times between the most widely spaced nodes may exceed a bit time. Furthermore, a high transmission rate results in steeper flanks of the transmitted signal, which in turn results in higher radiant emittance and thus poorer EMC properties of the communication system.